Two pleated filter composite having cushioning layers

ABSTRACT

A filter includes a pleated filter element having longitudinally extending pleats and a wrap member wrapped around the filter element. The wrap member is joined to the peaks of the pleats and has openings for increasing the dirt capacity of the filter. The filter element may be a composite of a filter layer, upstream and downstream support and drainage layers, a cushioning layer between the upstream support and drainage layer and the filter layer, and polymeric beads on the downstream side of the downstream support and drainage layer. An extruded polymeric mesh may comprise one or both of the upstream and downstream support and drainage layers.

This application is a continuation of application Ser. No. 08/091,928,filed on Jul. 16, 1993, now abandoned, which is a continuation of priorapplication Ser. No. 07/733,625, filed Jul. 22, 1991, now U.S. Pat. No.5,252,207 which is a continuation-in-part of prior application Ser. No.07/559,335, filed on Jul. 30, 1990, now abandonded, which is acontinuation-in-part of prior application Ser. No. 07/323,217, filed onMar. 15, 1989, now U.S. Pat. No. 5,084,178 which is a continuation ofprior application Ser. No. 07/206,676, filed on Jun. 15, 1988, nowabandoned.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a filter and more particularly to acorrugated filter for removing one or more substances from a fluidflowing through the filter. It also relates to a filter having a highdirt capacity and enhanced fatigue resistance.

BACKGROUND OF THE INVENTION

In filtration systems which have repeated or cyclical fluctuations inthe flow rate across a filter, fatigue failure of the filter can be aproblem. This is especially true for systems with wide flow excursions,e.g., from zero to full flow and back to zero, such as are experiencedin filtration systems for piston-type pumps as used in fluid powersystems. The flow cycles cause coincident cycles in the differentialpressure across the filter, typically resulting in a "breathing type"flexure within the pleated medium of the filter. If the pleated mediumis a composite having a filter layer and a support and drainage layer,as the pleated medium flexes, the support and drainage layer can rubback and forth along the filter layer. Because the support and drainagelayer is typically much more coarse than the filter layer, this rubbingmay produce weak spots which can rupture in service. This type offailure is known as a fatigue failure.

Another problem of conventional filters is that they may have a low dirtcapacity when the liquid flows through the filter element unevenly. Forexample, more liquid may flow through the upper portion of a filterelement than through the lower portion. Consequently, more dirt isdeposited on the upper portion of the filter element than on the lowerportion. This uneven loading of the filter element can lower the dirtcapacity of the filter element. The lower the dirt capacity of a filterelement, the more often it is necessary to replace the filter, resultingin increased material and labor costs.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a filterhaving good resistance to fatigue failures.

It is another object of the present invention to provide a filter havinga high dirt capacity.

It is still another object of the present invention to provide a filterwhich is highly reliable and has an extended service life.

According to one aspect of the present invention, a filter may comprisea porous, pleated filter element having first and second ends andlongitudinal pleat axis extending between the first and second ends. Thepleated filter element includes a composite having first and secondlayers wherein the first layer includes a filter medium. Each pleatincludes an open end, a bight end, and opposing sides which extendbetween the open end and the bight end. The filter further comprisesseveral polymeric beads which extend along the second layer opposite thefirst layer and generally perpendicular to the pleat axis. Each beadextends from the open end of the pleat along the first side to the bightend and from the bight end along the second side to the open end. Theportions of each bead which extend along the first and second sides ofthe pleat are joined to one another. Further, the filter comprises firstand second end caps joined to the first and second ends of the pleatedfilter element.

A filter embodying this aspect of the invention provides more reliableservice and a greater service life than many conventional filters. Thesecond layer may be a downstream support and drainage layer. A supportand drainage layer typically has greater mechanical strength ortoughness than the filter layer, which is frequently delicate because,for example, of its high degree of porosity. Consequently, by disposingthe polymeric beads on the surface of the downstream support anddrainage layer rather than directly on the filter layer, the filterlayer is protected from tearing or excessive distortion when the filterelement is corrugated or used to filter fluids. Furthermore, by joiningthe opposing portions of each bead within the pleats, flow channels aredefined within each pleat. These flow channels are maintained relativelyopen by the joined portions of the beads even when the filter issubjected to high pressure liquids or pulsating flow.

According to another aspect of the present invention, a pleated filterelement may comprise a filter layer, a support and drainage layer, and acushioning layer. The support and drainage layer is disposed along oneside of the filter layer. The cushioning layer is positioned between thesupport and drainage layer and the filter layer and includes a materialwhich is smoother than the support and drainage layer.

According to a further aspect of the present invention, a filter elementmay comprise a pleated composite having a filter layer and a support anddrainage layer. In addition, the composite has a material positionbetween the filter layer and the support and drainage layer forminimizing abrasion of the filter layer by the support and drainagelayer.

A filter element embodying these aspects of the present invention isparticularly reliable. The cushioning layer or material between thefilter layer and the support and drainage layer prevents the support anddrainage layer from abrading the filter layer and producing a weak spotin the filter layer. Consequently, a filter embodying the presentinvention resists fatigue failures far better than conventional filters.

According to yet another aspect of the present invention, a filter maycomprise a pleated filter element and a wrap member. The pleated filterelement has longitudinally extending pleats having peaks. The wrapmember is wrapped around the filter element, is joined to the peaks ofthe pleats, and has openings, thereby increasing the dirt capacity ofthe filter element. The total area of the openings is less than one halfof the total area of the surface defined by the peaks of the pleats.

A filter element embodying this aspect of the invention not only has anincreased dirt capacity, but it also has superior fatigue failureresistance, especially when used in systems with large, frequent changesin flow rates. By wrapping the pleats with the wrap member, movement ofthe pleats is restrained and abrasion of the filter medium is therebyprevented. In addition, the wrap member produces a more uniform flowdistribution over the length of the filter. Consequently, dirt is moreevenly deposited on the filter element, increasing the useful life ofthe filter. The wrap member also helps the filter to resist radiallyoutwardly direct forces and can prevent the filter element from swellingoutward.

According to an additional aspect of the invention, a filter element maycomprise a pleated composite which includes two extruded polymeric meshlayers and a filtering layer positioned between them.

According to another aspect of the invention, a filter element maycomprise a pleated composite and a wrap which is wrapped around thepleated composite. The pleated composite includes an extruded polymericmesh layer and a filtering layer.

Filter elements embodying these aspects of the invention are easy tomanufacture and highly effective. With the extruded polymeric meshlayers forming part of the pleated composite, the pleated composite caneasily be fabricated and corrugated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut-away elevation of an embodiment of a filterequipped with a wrap member according to the present invention.

FIG. 2 is a transverse cross-sectional view of a sector of theembodiment of FIG. 2.

FIG. 3 is a perspective view of a filter element for use in the presentinvention prior to corrugation.

FIG. 4 is an elevation of a portion of the filter element of FIG. 3after corrugation as viewed from the downstream side of the element.

FIG. 5 is a cross-sectional view of the filter element of FIG. 4 takenalong Line V--V of FIG. 4.

FIG. 6 is an elevation of another embodiment of a filter according tothe present invention with the wrap member partially removed.

FIG. 7 is an elevation of another embodiment of a filter according tothe present invention.

FIG. 8 is a perspective view of another embodiment of a filter accordingto the present invention.

FIG. 9 is an elevation of another embodiment of a filter according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A number of preferred embodiments of a filter according to the presentinvention will now be described while referring to the accompanyingdrawings. FIG. 1 is a perspective view of a first embodiment equippedwith a spiral wrap member, and FIG. 2 is a transverse cross-sectionalview of a sector of the embodiment of FIG. 1. As shown in FIG. 1, thefilter 10 of this embodiment has a hollow pleated filter element 20 withlongitudinal pleats. A hollow, rigid tubular core 11 may be disposedinside the hollow center of the filter element 20 to give the filterelement 20 sufficient strength to resist the inwardly directed forceswhich act on the filter element 20. The core 11 can be made of anysufficiently strong material which is compatible with the fluid to befiltered. For example, the illustrated core 11 is made of a perforatedmetal, but, alternatively, it can be made of a polymeric material.

A blind end cap 12 and an open and cap 13 may be fitted over the twoends of the filter element 20 to direct the fluid through the filterelement 20, Alternatively, both end caps can be open or can includeconnectors to link a stack of filter elements. The end caps 12 and 13may be fashioned from any suitably impervious material, such as ametallic or polymeric material, which is compatible with the fluid to befiltered. The end caps 12 and 13 may be secured to the ends of thefilter element 20 by any suitable means, including a bonding agent suchas an adhesive or a potting compound Alternatively, the end caps 12 and13 may be melt-bonded to the ends of the filter element 20 or joined bymeans of spin bonding or sonic welding. The ends of the hollow core 11may be secured to the two end caps 12 and 13 by similar means.

The filter element 20 itself can be configured in a variety of wayswithout departing from the scope of the invention. For example, thefilter element can have an upstream support and drainage layer, a filterlayer, and a downstream support and drainage layer. However, the presentinventors found that the fatigue resistance of a filter element can begreatly increased by the provision of a cushioning layer between thefilter layer and either or both of the support and drainage layers. FIG.2 illustrates an example of such a filter element 20. It has amulti-layer, composite construction including an upstream support anddrainage layer 21, a cushioning layer 22, a filter layer 23, and adownstream support and drainage layer 24. The exemplary filter elementillustrated in FIG. 2 also includes polymeric beads 25 disposed on thedownstream surface of the downstream support and drainage layer 24.

The support and drainage layers are preferably very open, allowing fluidto flow laterally and to uniformly distribute the fluid across thesurface of the filter layer. Thus, the support and drainage layerstypically have a low edgewise flow resistance. The support and drainagelayers also prevent the pleated surfaces of the filter from coming intocontact with one another and thereby reducing the effective surface areaof the filter layer 23. The support and drainage layers do so byproviding a positive spacing (fanning) between adjacent pleats of thefilter layer.

Any suitable woven or nonwoven material having good porosity can be usedfor the upstream support and drainage layer 21 as well as the downstreamsupport and drainage layer 24. Furthermore, either layer may befabricated from one or more of natural fibers, polymeric materials, andglass. In a preferred embodiment, the upstream support and drainagelayer 21 comprises an extended polymeric mesh. The mesh can befabricated from any polymeric material, including polyester,polypropylene, or polyamide such as nylon, which is suitable for thefluid being filtered and for the applicable filtration parameters suchas temperature. For example, polypropylene might be preferable to nylonfor filtering hot water. The thickness of the mesh is preferably in therange from about 0.010 to about 0.025 of an inch but may be less than0.010 of an inch or more than 0.025 of an inch. The number of strandsper inch is preferably in the range from about 10 to about 30 in eachlinear dimension but may be less than 10 or more than 30. For example,the mesh may have up to 80 or more strands per inch in each lineardimension. The mesh is preferably as smooth as possible to reduceabrasion between it and the underlying layers. Extruded polymeric meshis generally preferable to other support and drainage materials,including woven and nonwoven fibrous webs and polymeric netting, becauseit is so smooth and because it typically does not shrink duringfabrication and corrugation of the filter element. An extruded polymericmesh available from Nalle Corporation is particularly smooth. Forexample, it has no significant irregularities such as knobs, at theintersections of the strands of the mesh which might otherwise abradethe filter layer. A nylon mesh available from Nalle Corporation underthe trade designation NIF020S 13×13, where 020 indicates the thicknessin thousandths of an inch and 13×13, indicates the number of strands perlinear inch in the x and y directions, is especially preferred. Anotherexample of a suitable material for the upstream support and drainagelayer is a nylon sheathed polyester nonwoven material sold by BASF ofWilliamsburg, Va. under the trade designation Colback 50. However, aNalle extruded mesh is preferable to Colback 50 because it is lessabrasive and results in a significantly higher dirt capacity.

A principal purpose of the cushioning layer 22 is to prevent abrasionbetween the support and drainage layer and the filter layer. The supportand drainage layer typically has good drainage properties because it isfashioned from relatively large fibers or filaments. Consequently, itgenerally has a rougher surface than the filter layer. When such amaterial is laminated directly to the filter layer 23, significantabrasion of the filter layer 23 results when the filter element 20undergoes flexing, for example, due to pressure cycles, and the supportand drainage layer repeatedly rubs against the filter layer. However,when a cushioning layer 22 which is smoother than the upstream drainagelayer is interposed between the support and drainage layer and thefilter layer 23, the abrasion of the filter layer 23 can be greatlyreduced, resulting in an increase in the useful life of the filterelement 20.

The cushioning layer 22 is preferably formed of a thin, very porousmaterial. For example, the cushioning layer preferably has a thicknessof less than 100 micron. It is also preferably formed from a materialwhich can be characterized as smooth or as smooth and tough. Forexample, it may be a nonabrasive, nonwoven material with a high tensilestrength. A preferred material for the cushioning layer 22 is a wet-laidpolyester nonwoven material sold by Hirose Corporation under the tradedesignation 05TH08. Other preferred materials include a nylon nonwovenmaterial available from Fiberweb North America Inc. under the tradedesignation Cerex and a nonwoven polyester material available fromReemay Corporation under the trade designation Reemay, such as Reemay2006 or Reemay 2250. Of these materials, the materials from Hirose andReemay are most preferred. However, any suitable woven or nonwovenmaterial which is smoother (less abrasive) than the upstream drainagelayer 21 may be used,

The filter layer 23 may be selected in accordance with several factors,including the nature of the fluid being filtered, the nature and size ofthe contaminants in the fluid, and the acceptable pressure drop acrossthe filter element 20. The filter layer 23 may be any suitable medium.For example, the filter medium may be fashioned as a membrane or a wovenor nonwoven fibrous sheet and may be fabricated from a natural orsynthetic polymer or glass. Thus, the filter medium may comprise anonwoven sheet principally including cellulose fibers or essentiallyconsisting of glass fibers with a resin binder. Furthermore, the filtermedium may have any desired pore structure including a graded porestructure, and any desired rated pore size. However, the rated pore sizeof the filter layer 23 is preferably less than the rated pore size ofthe upstream or downstream support and drainage layers. In a preferredembodiment, the filter layer 23 comprises a suitable grade of a glassfiber acrylic bonded medium with an integral substrate providingadditional strength. Preferred media, including a family of fibrousfilter media having various binder resins, ere available from PallCorporation under the trade names Ultipor and Pallflex.

The downstream support and drainage layer 24 typically has greatermechanical strength than the filter layer 23 and therefore serves toprotect the more delicate filter layer 23 from tearing or distortionduring corrugation or use. One example of a suitable material for use asthe downstream drainage layer 24 is a paper available from DexterCompany under the trade designation T-244.

As shown in FIG. 2, the filter element 20 may include polymeric beads 25formed on the downstream surface of the downstream support and drainagelayer 24 on each of the pleats 26 of the filter element 20. Within eachpleat 26, the beads 25 are joined to themselves and serve as spacers todefine flow channels 27 within the pleat 26 and ensure proper fluid flowthrough the pleat 26. It is also possible to provide polymeric beads 25on the upstream side of the filter layer 23 as well as on the downstreamside.

The polymeric beads 25 may be formed from a variety of materialsincluding many thermoplastic or thermosetting materials. Thus, thepolymeric beads 25 may be formed from a material comprising a polyester,polyamide, or polyolefin resin. Furthermore, the polymeric beads may beapplied in parallel strips along the downstream surface of thedownstream support and drainage layer 24 in any suitable manner. Forexample, the polymeric beads 25 may be formed from a hot melt adhesiveand applied continuously from an evenly spaced multi-orifice dispensinghead with the downstream support and drainage layer 24 moving under thedispensing head, preferably at a constant velocity, producing severalcontinuous, parallel beads. The hot melt adhesive may be applied to thedownstream support and drainage layer 24 either before or after filterelement 20 has been formed into a composite.

In a modification of this method, the hot melt adhesive may be appliedintermittently from the dispensing head or from an unevenly spacedmulti-orifice dispensing head to produce several discontinuous, parallelbeads or several unevenly spaced parallel beads. In other alternatives,a granular polymeric material may be applied by extrusion from amulti-orifice extrusion head; a plastisol polyurethane may be appliedfrom a multi-orifice dispenser and then cured with an in-line heatingdevice; or a solvent based adhesive or potting compound may be appliedfrom a multi-orifice dispenser and the solvent may then be flashed by aheating/ventilation device.

As applied to a support and drainage layer 24, the bead materialpreferably has a surface tension high enough to prevent excessivewetting of the support and drainage layer 24 or wicking through thesupport and drainage layer 24 but not so high as to prevent adhesionbetween the beads 25 and the support and drainage layer 24. Thisminimizes flow restriction through the exemplary filter element sincethe surface of the support and drainage layer 24 which is in contactwith the beads 25 is effectively blocked. The contact angle between thebeads 25 and the downstream drainage layer 24, as measured by theSessile method, may preferably be in the range from about 100° to about120°.

Various cross-sectional shapes of the beads 25 are suitable. The mostpreferred shape has a needle-like cross section. This shape minimizesthe contact area between the bead 25 and the support and drainage layer24. However, this shape is difficult to produce at reasonable productionrates. For large scale production, a generally circular cross section ispreferred. Other suitable shapes include triangular, diamond, square,and rectangular cross sections.

The size of each bead 25 and the spacing between the beads 25 may varywithout departing from the scope of the invention. The size of the beads25 is determined by the size of the orifice in the dispensing head, therelative velocity between the dispensing head and the downstreamdrainage layer 24, and the viscosity of the bead material. For manyapplications, the diameter of the beads may preferably be in the rangefrom about 4 to about 20 mils.

The spacing between beads 25 is preferably selected so that the stressdeformation, i.e., deflection, of the pleated composite satisfies bothof the following conditions: (1) the elastic limit of the filter mediumcomprising the filter layer 23, i.e., the maximum unit of stress beyondwhich the filter medium will not return to its original shape, is notexceeded and (2) the deflection of the composite during normal operationdoes not increase the flow resistance in the flow channels 27 more than10 percent. For many applications, the spacing between evenly spacedbeads 25 is preferably such that about 5 to about 20 beads per inch or,more preferably, about 8 to about 15 beads per inch are applied to thedownstream drainage layer 24.

Once the beads 25 have been applied to the downstream support anddrainage layer 24, then the upstream support and drainage layer 21, thecushioning layer 22, the filter layer 23, and the downstream support anddrainage layer 24 with the beads 25 are fed into a corrugator, such as aChandler "grab and fold" type corrugator or a Rabofsky "cam actuatedblade" type corrugator. The various layers of the filter element may beformed into a composite before being fed into the corrugator, or layersincluding the downstream support and drainage layer 24 with the beads 25may be fed individually into the corrugator, which then forms thecomposite at the same time it forms the pleats 26 in the filterarrangement 10. It is typically preferable to preheat the extrudedpolymeric mesh before it enters the corrugator so it will set well afterthe composite has been corrugated.

FIG. 3 is a perspective view of an example of a composite filter element20 prior to corrugation, FIG. 4 is an elevation of a portion of thefilter element 20 after corrugation, and FIG. 5 is a transversecross-sectional view taken along Line V--V of FIG. 4 of a portion of thecorrugated filter element 20. As shown in FIGS. 4 and 5, each pleat 26extends generally perpendicularly to the beads 25 and includes an openend 26a, a bight end 26b, and first and second opposing sides 26c, 26d.The portions of each bead 25 which extend along the opposing sides 26c,26d of each pleat 26 are joined to one another, defining flow channels27 within each pleat 26 between adjacent beads 25 and the opposing sides26c, 26d. Because the downstream support and drainage layer 24 and beads25 are preferably positioned on the downstream surface of the filterlayer 23 to resist the pressure drop across the filter 10 during normaloperation, the flow channels 27 are preferably drainage channels.

Care should be taken in the alignment of the support and drainage layer24 within the corrugator to ensure that the beads 25 oppose themselvesin the pleats 26 so the opposing portions of the beads 25 can be joined.If the beads 25 are formed from a hot melt adhesive, heated panels inthe corrugator may be used to tack the beads together. Beads comprisingother types of materials may require coating by an adhesive or softeningby a solvent for this purpose. After the filter element 20 has beencorrugated, it may be desirable to set the tacked beads in a forcedconvection oven. It may also be desirable to cure any binders in thefilter medium of the filter layer 23 at the same time the beads 25 arebeing set. Alternatively, the beads 25 may be set and the filter mediummay be cured in a tunnel oven during a continuous production process. Ofcourse, the setting of the beads 25 and the curing of the filter mediumshould be done at temperatures which are not deleterious to the othercomponents of the filter. Furthermore, all of the cured components ofthe filter element should be compatible with the fluid to be filtered.

In corrugating the filter element 20 and setting the beads 25, each bead25 in the pleat 26 is preferably joined to itself the entire distancefrom the bight end 26b to the open end 26a of the pleat 26. Furthermore,the radius at the bight end 26b of the pleat 26 is preferably as smallas possible, and preferably zero, to maximize resistance to fatiguefailure which may result from flexure of the filter element 20 duringpulsating flow conditions. However, the beads 25 must not beover-compressed, since over-compression would cause excessive blindingof the filter element 20 and would reduce the cross-sectional area ofthe flow channel 27. Thus, when corrugating the filter element 20, itmay be desirable to secure the filter element 20 in a spring-loadedfixture with positive stops to prevent over-compression and a slightreverse-curve to ensure the minimum radius at the bight end 26b of thepleat 26.

By joining the opposing portions of each bead 25, the flow channels 27within each pleat 26 remain relatively open even when the filter 10 isused to filter a pulsating flow at high differential pressures. Thus, afilter element according to the present invention has a greaterresistance to flow fatigue and therefore provides more reliable serviceand a greater service life than many conventional filters.

Alternatively, the downstream support and drainage layer may comprise anextruded polymeric mesh such as that described with respect to theupstream support and drainage layer. For example, the downstream supportand drainage layer may be an extruded mesh available from NalleCorporation, such as the extruded nylon mesh available under the tradedesignation NIF020S 13×13.

If the extruded mesh is sufficiently smooth, it may be preferable not toinclude a cushioning layer between the filtering layer and thedownstream extruded mesh layer. Alternatively, a cushioning layer may bepositioned between the filtering layer and the downstream mesh. Thecharacteristics of the cushioning layer between the filtering layer andthe downstream mesh are very similar to those of the cushioning layerbetween the filtering layer and the upstream mesh. However, thedownstream cushioning layer also preferably has sufficient strength towithstand the forces associated with the pressure drop across thefiltering layer. The preferred materials listed for the upstreamcushioning layer are also the preferred materials for the downstreamcushioning layer.

A number of preferred examples of composite pleated filter elements arelisted below.

    ______________________________________                                        Element A                                                                     Upstream s/d layer Nalle extruded mesh                                                           (NIF.013-13-13)                                            Cushioning layer   Hirose wet-laid                                                               polyester nonwoven                                                            (05TH08)                                                   Filter layer       Pall Ultipor medium                                                           (suitable grade)                                           Downstream s/d layer                                                                             Dexter Company T-244                                       Polymeric bead spacers                                                                           Hot-melt adhesive                                          Element B                                                                     Upstream s/d layer Nalle extruded mesh                                                           (NIF020S 13 × 13)                                    Cushioning layer   Reemay 2006 nonwoven                                                          polyester                                                  Filter layer       Pall Ultipor medium                                                           (suitable grade)                                           Cushioning layer   Cerex nylon nonwoven                                                          (suitable grade)                                           Downstream s/d layer                                                                             Nalle extruded mesh                                                           (N1F020S 13 × 13)                                    Element C                                                                     Upstream s/d layer Nalle extruded mesh                                                           (NIF.013-13-13)                                            Cushioning layer   Cerex nylon nonwoven                                                          (.4 oz/sq. yard)                                           Filter layer       Pall Ultipor medium                                                           (suitable grade)                                           Downstream s/d layer                                                                             Dexter Company T-244                                       Polymeric bead spacers                                                                           Hot-melt adhesive                                          ______________________________________                                    

Of these five examples, Elements A and B are the most preferred partlybecause the Nalle mesh has greater dirt capacity than Colback 50.

One of the major limiting factors on the life of a filter is the dirtcapacity of the filter element of the filter. When the filter elementbecomes loaded with dirt, it is usually necessary to replace the filter.Frequent replacement of a filter is uneconomical due to both the cost ofthe filter and the cost of the labor involved in its replacement.

The present inventors discovered that if a pleated filter element isenveloped in a wrap member having openings, the dirt capacity of thefilter element can be greatly increased compared to that of an unwrappedpleated filter element or compared to that of a pleated filter elementcompletely enveloped in a wrap member.

There may be several reasons why the dirt capacity is increased. Thewrap member may help to maintain the spacing between adjacent pleats ofthe filter element. For example, in a clean, unwrapped filter, a flowdrag force on the apexes of the pleats can cause some of the adjacentpleats to pinch together. This reduces the effective surface area andtherefore the useful life of the filter. By providing the filter with awrap member which is joined to the peaks of the pleated filter element,adjacent pleats are restrained from pinching together. By providing thewrap member in combination with the polymeric bead spacers, the pleatsare restrained even further. Therefore, the effective surface area ofthe filter is maximized and the useful life is significantly increased.

A wrap member also restrains movement of the pleats of a filter elementwhen subjected to cyclic pressure fluctuations. As a result, abrasioncaused by movement of the pleats is decreased, and the life span of thefilter element is further increased.

In addition, the wrap member may produce a more uniform flowdistribution over the length of the filter. In an unwrapped filter, flowthrough the filter element can be uneven. For example, when a filterelement is enclosed in a housing, flow through the filter element may begreatest in the area closest to the inlet of the filter housing. Unevenflow causes dirt to be unevenly deposited on the filter element, and theuneven distribution can reduce the useful life of the filter. Byproviding the filter with a wrap member having openings, the flow can bedistributed more evenly along the filter element, increasing the usefullife of the filter.

The results produced by a wrap member are striking. For example, afilter element wound with a wrap member according to the presentinvention is expected to have a dirt capacity about 10% to 20% higherthan the dirt capacity of a similar unwrapped filter element.

The wrap member also helps a filter element to resist radially outwardlydirected forces and can prevent the filter element from swelling outwardduring pressure fluctuations in which the filter element is momentarilysubjected to a negative differential pressure.

FIG. 1 illustrates an example of the use of a wrap member with a filteraccording to the present invention. In the embodiment of FIG. 1, thefilter 10 is equipped with a wrap member 30 wrapped around the filterelement 20 and having openings formed therein for the passage of fluid.In this embodiment, the wrap member 30 is a parallel-sided strip 31 offlexible material which is spirally wrapped about the filter element 20in a plurality of turns. The spiral turns have a pitch greater than thewidth of the strip 31 so the openings in the wrap member comprise aspiral gap 32 between adjacent turns. It can be seen from FIG. 1 thatthe openings are unobstructed. The spiral strip 31 may be made of anysuitable material which is compatible with the fluid the being filtered.Since much of the fluid being filtered reaches the filter elementthrough the openings in the wrap member, the wrap member need not bepermeable to the fluid, although in a preferred embodiment it ispermeable. For many applications, a porous, polymeric, nonwoven materialavailable from Reemay Corporation under the trade designation Resmay issuitable. Laminates of the Reemay material can also be employed.Examples of other suitable material are oil board paper and mylar film.The material can be selected in accordance with the desired reverse flowstrength of the filter element.

The spiral strip 31 can be secured to the outer surface of the filterelement 20 by any suitable means. One means of attaching the spiralstrip 31 to the filter element 20 is by a bonding agent, such as a hotmelt adhesive, which is applied to the strip 31 as it is wound aroundthe filter element 20. The bonding agent 33 can be applied to the strip31 in the form of a continuous or intermittent bead which spirals aroundthe filter element 20 parallel to the edges of the strip 31.Alternatively, the strip 31 may be fusion bonded to the filter element20 by a hot wheel which travels down the filter as the filter rotates.

The openings of the wrap member are preferably distributed uniformlyalong the filter element 20, although a nonuniform distribution may beused. To prevent the wrap member from becoming loaded, the size of theopenings should be large enough to allow the passage of virtually all ofthe particles contained in the fluid being filtered. Furthermore, thetotal area of the openings is generally less than 50% of the totalsurface area of the surface defined by the peaks of the pleats, e.g.,the cylinder circumscribing the peaks of the pleats of the illustratedfilter element. More preferably the total area of the openings is in therange from about 6% to about 30% of the total area of the surfacedefined by the peaks of the pleats. For example, in one embodiment, thefilter element has a 41/2" outer diameter and an 81/4" length, thespiral strip 31 has a 11/2" width, and the spiral gap 32 betweenadjacent turns has a 1/4" width.

The filter 10 of FIG. 1 can be manufactured in any suitable manner. Forexample, a composite filter element 20 having a standard axial length(typically 42") can be formed using a corrugator in substantially thesame manner as described previously. The core 11 is then inserted intothe filter element 20 and the assembly is mounted on a mandrel. Whilethe filter element is rotated on the mandrel, a spiral strip 31 iswrapped around the filter element 20 so as to leave a gap 32 of adesired size between turns. As the strip 31 is wrapped around the filterelement 20, a hot melt adhesive 33 is applied to the inner surface ofeither the strip 31, the outer surface of the filter element 20, or bothto bond the strip 31 to the filter element 20. Alternatively, a hotwheel may be run along an edge of the strip to fuse the strip to thepeaks of the pleats. The wrapped filter element 20 is then cut to asuitable length and the end caps 12 and 13 are fitted over the ends ofthe filter element 20 and the spiral strip 31. The flanges of the endcaps 12 and 13 fit over the ends of the spiral strip 31 and prevent itfrom unwinding.

FIG. 6 illustrates another embodiment of the present invention. Theembodiment has a wrap member 40 in the form of a spiral strip 41 havingopenings in the form of perforations 44 formed in the strip 41 itself.These perforations 44 serve the same function as the spiral gap 32 ofthe embodiment of FIG. 1 and increase the dirt capacity of the filterelement 20. The perforations 44 are preferably formed in the spiralstrip 41 prior to its being wrapped around the filter element 20, sincepunching the perforations 44 in the strip 41 after wrapping could damagethe filter element 20. The adjacent turns of the perforated spiral strip41 can be separated from one another by a spiral gap, as in theembodiment of FIG. 1, so the openings comprise both the perforations andthe spiral gap. However, the wrap member 40 may have greater strength ifthe edges of adjacent turns partially overlap one another, as shown inFIG. 6. The spiral strip 41 has a first edge 42 and a second edge 43.The first edge 42 may be bonded directly to the filter element 20 with abonding agent 45, while the second edge 42 may overlap and be bonded tothe first edge 43 of the adjacent turn of the strip 41. The structure ofthis embodiment is otherwise substantially the same as that of theembodiment of FIG. 1.

The wrap member need not be wrapped spirally around the filter element20. FIG. 7 is an elevation of another embodiment of the presentinvention having a wrap member comprising a plurality of strips 51 of aflexible material which are wrapped circumferentially around the filterelement 20 in a plurality of parallel turns. Adjacent turns of thestrips 51 are separated from one another by circumferentially-extendinggaps 52 which comprise the openings. The ends of each strip 51 overlapand are bonded to one another, and the strips 51 can also be attached tothe filter element 20 by bonding. The circumferentially-extending gaps52 of this embodiment function in the same manner as the spiral gap 32of FIG. 1 and increase the dirt capacity of the filter element 20.Although a wrap member 50 with circumferentially extending strips 51 iseffective for increasing the dirt capacity of the filter, such a filteris more complicated to manufacture than a filter having a spiral wrapmember, and therefore a filter with a spiral wrap member is generallymore economical than one of the type illustrated in FIG. 7.

The embodiments of FIGS. 1 and 6 employ only a single spiral strip toform the wrap member. FIG. 8 illustrates another embodiment of thepresent invention which differs from the embodiment of FIG. 1 in that ithas a wrap member 60 which comprises two strips 61 and 62 which arespirally wound around the filter element 20 in parallel each stripforming a plurality of turns. The strips are separated by spiral gaps 63which comprise the openings 61. The structure of this embodiment isotherwise the same as that of the embodiment of FIG. 1. There is nolimit on the number of strips which constitute the spiral wrap.

FIG. 9 illustrates another embodiment of the present invention having awrap member 70 in the form of a strip 71 of mesh which is wrappedspirally around a filter element. In this embodiment, the openings inthe wrap member 70 are constituted by the mesh openings 72. The size ofthe mesh will depend upon the properties of the fluid being filtered,the flow rate, and other factors, but a mesh with a mesh size of about30 counts per inch is generally satisfactory. The material which is usedfor the mesh will depend on the type of fluid being treated. Examples ofsuitable types of mesh are a knitted sock or a polymeric mesh. Apolymeric mesh has the advantage that it can be directly connected tothe filter element 20 by fusion bonding without the need for anadhesive. The structure of this embodiment is otherwise the same as thatof the embodiment of FIG. 1.

In the exemplary embodiments, the filter element is intended for usewith outside-in radial fluid flow. However, if the positions of theupstream and downstream support and drainage layers 21 and 24, thecushioning layer 22, and the polymeric beads 25 with respect to thefilter layer 23 are switched, the filter element can be used forinside-out radial flow. In a filter element for inside-out radial flowaccording to the present invention, the upstream support and drainagelayer would extend along the inner surface of the filter layer 23 (thesurface closest to the radial center of the filter), the cushioninglayer would be positioned between the upstream support and drainagelayer and the filter layer, and the downstream support and drainagelayer would extend along the outer surface of the filter layer 23 withthe polymeric beads 25 adhered to the outer surface of the downstreamsupport and drainage layer rather than to the inner surface.

Although the present invention has been described in terms of exemplaryembodiments and examples, it is not limited to those embodiments orexamples. Alternative embodiments, examples, and modifications whichwould still be encompassed by the invention may be made by those skilledin the art, particularly in light of the foregoing teachings. Therefore,the following claims are intended to cover any alternative embodiments,examples, modifications, or equivalents which may be included within thespirit and scope of the invention as defined by the claims.

What is claimed is:
 1. A filter element comprising:a pleated compositeincluding first and second support and drainage layers, each support anddrainage layer including a polymeric mesh, layer filter layer positionedbetween the first and second mesh layers, a first cushioning layersmoother than the first mesh layer positioned between the first meshlayer and the filter layer, and a second cushioning layer smoother thanthe second mesh layer positioned between the second mesh layer and thefilter layer, wherein the filter layer has a pore size less than thesupport and drainage layers in the composite and wherein each saidcushioning layer comprises a material constructed so as to substantiallyprevent the respective, adjacent support and drainage layer fromabrading the filter layer.
 2. A filter element as claimed in claim 1wherein each support and drainage layer comprises an extruded polymericmesh.
 3. A filter element as claimed in claim 1 wherein for each meshlayer the number of strands in the x and y directions is in the range offrom about 10 to about 30 per inch.
 4. A filter element as claimed inclaim 1 wherein each support and drainage layer comprises polyester,polypropylene, or polyamide.
 5. A filter element as claimed in claim 1further comprising a member enveloping the pleated composite wherein themember comprises a polymeric mesh.
 6. A filter element as claimed inclaim 5 wherein the member enveloping the pleated composite comprises astrip of polymeric mesh wrapped around the pleated composite.
 7. Afilter element as claimed in claim 5 wherein the pleated compositeincludes pleats having peaks and the member enveloping the pleatedcomposite is connected to the peaks of the pleats.
 8. A filter elementas claimed in claim 1 wherein each cushioning layer is made of adifferent material from the filter layer.
 9. A filter element as claimedin claim 1 wherein each cushioning layer comprises a smooth, porousnonwoven material.
 10. A filter element as claimed in claim 9 whereinthe filter layer comprises a fibrous medium.
 11. A filter element asclaimed in claim 10 further comprising a polymeric mesh memberenveloping pleated composite.
 12. A filter element as claimed in claim11 wherein the polymeric mesh member envelops the pleated filter elementin a configuration which helps maintain the spacing between adjacentpleats of the filter element.
 13. A filter element as claimed in claim12 wherein the pleated composite includes peaks and wherein theconfiguration comprises the polymeric mesh member joined to the peaks.14. A filter element as claimed in claim 12 wherein the fibrous mediumcomprises glass fibers and a resin binder.
 15. A filter element asclaimed in claim 9 wherein at least one of the cushioning layerscomprises a nonwoven polyester material available from ReemayCorporation under the trade designation Reemay.
 16. A filter element asclaimed in claim 9 wherein at least one of the cushioning layerscomprises a nylon nonwoven material available from Fiberweb NorthAmerica under the trade designation Cerex.
 17. A filter element asclaimed in claim 1 wherein the filter layer is discrete from at leastone of the cushioning layers.
 18. A filter element as claimed in claim17 wherein the filter layer is discrete from both cushioning layers. 19.A filter element comprising a pleated composite having a filter layerhaving first and second sides, first and second polymeric support anddrainage layers disposed on the first and second sides of the filterlayer, and first and second cushioning layers disposed between thefilter layer and the first and second support and drainage layers,respectively, for resisting abrasion of the filter layer by the supportand drainage layers, each of the cushioning layers being made of adifferent material from the filter layer, wherein the filter layer has apore size less than the support and drainage layers in the composite andwherein each said cushioning layer comprises a material constructed soas to substantially prevent the respective, adjacent support anddrainage layers from abrading the filter layer.
 20. A filter element asclaimed in claim 19 wherein each support and drainage layer comprises apolymeric mesh and the filter layer comprises a fibrous medium.
 21. Afilter element as claimed in claim 20 further comprising a polymericmesh member enveloping the pleated composite.
 22. A filter element asclaimed in claim 21 wherein the polymeric mesh member enveloping thepleated composite comprises a strip of polymeric mesh wrapped around thepleated composite.
 23. A filter element as claimed in claim 19 whereineach of the support and drainage layers comprises an extruded polymericmesh.
 24. A filter element as claimed in claim 19 wherein eachcushioning layer comprises a smooth, porous, nonwoven polymericmaterial.
 25. A filter element as claimed in claim 24 wherein the filterlayer comprises a fibrous medium.
 26. A filter element as claimed inclaim 25 further comprising a polymeric mesh member enveloping thepleated composite.
 27. A filter element as claimed in claim 26 whereinthe polymeric mesh member envelops the pleated filter element in aconfiguration which helps maintain the spacing between adjacent pleatsof the filter element.
 28. A filter element as claimed in claim 27wherein the pleated composite includes peaks and wherein theconfiguration comprises the polymeric mesh member joined to the peaks.29. A filter element as claimed in claim 27 wherein the fibrous mediumcomprises glass fibers and a resin binder.
 30. A filter element asclaimed in claim 24 wherein at least one of the cushioning layerscomprises a nylon nonwoven material available from Fiberweb NorthAmerica under the trade designation Cerex.
 31. A filter element asclaimed in claim 19 wherein the filter layer is discrete from at leastone of the cushioning layers.
 32. A filter element as claimed in claim31 wherein the filter layer is discrete from both cushioning layers. 33.A filter element as claimed in claim 19 wherein each support anddrainage layer comprises polyester, polypropylene, or polyamide.
 34. Afilter element comprising:a pleated composite including first and secondsupport and drainage layers, each support and drainage layer comprisinga polymeric mesh, a filter layer positioned between the first and secondsupport and drainage layers, said filter layer comprising a resin bondedfibrous medium and an integral substrate, and a cushioning layersmoother than the first support and drainage layer positioned betweenthe first support and drainage layer and the filter layer, wherein thefilter layer has a smaller pore size than the first and second supportand drainage layers and wherein said cushioning layer comprises a porousmaterial constructed so as to substantially prevent the first supportand drainage layer from abrading the filter layer.
 35. A filter elementas claimed in claim 34 wherein each polymeric mesh comprises an extrudedmesh.
 36. A filter element as claimed in claim 35 wherein each polymericmesh has a number of strands per inch in the range of from about 10 toabout
 30. 37. A filter element as claimed in claim 35 wherein eachpolymeric mesh has a number of strands per inch of greater than about30.
 38. A filter element as claimed in claim 34 wherein the thickness ofeach polymeric mesh is from about 0.010 to about 0.025 inch.
 39. Afilter element as claimed in claim 34 wherein the first support anddrainage layer in a filtering environment for which the filter elementis adapted is positioned upstream of said filter layer.
 40. A filterelement as claimed in claim 34 wherein the cushioning layer comprises anonwoven material.
 41. A filter element as claimed in claim 40 whereinthe nonwoven material comprises a nylon or a polyester.
 42. A filterelement as claimed in claim 34 wherein the cushioning layer comprises awet-laid polyester nonwoven material.
 43. A filter element as claimed inclaim 34 wherein the cushioning layer comprises a nylon nonwovenmaterial.
 44. A filter element as claimed in claim 34 wherein thefibrous medium comprises a resin bonded glass fiber medium.
 45. A filterelement as claimed in claim 34 further comprising a wrap member wrappedaround the pleated composite.
 46. A filter element as claimed in claim45 wherein the wrap member is spirally wound around the pleatedcomposite with a gap between adjacent windings.
 47. A filter element asclaimed in claim 34 wherein the first support and drainage layer ispositioned upstream of the filter layer and wherein the cushioning layercomprises a nonwoven material.
 48. A filter element as claimed in claim34 wherein the first support and drainage layer is positioned upstreamof the filter layer in a filtering environment for which the filterelement is adapted and each polymeric mesh layer comprises an extrudedpolymeric mesh, wherein the cushioning layer comprises a nonwovenmaterial, and wherein the filter element further comprises a wrap memberwrapped around the pleated composite.
 49. A filter element as claimed inclaim 34 wherein each polymeric mesh comprises an extruded polymericmesh having a number of strands per inch in the range of from about 10to about 30, wherein the first support and drainage layer is positionedupstream of the filter layer in a filtering environment for which thefilter element is adapted, wherein the cushioning layer comprises anylon or polyester nonwoven material, and wherein the filter elementfurther comprises a wrap member spirally wrapped around the pleatedcomposite with a gap between adjacent windings of the wrap.
 50. A filterelement as claimed in claim 49 wherein the fibrous medium comprisesresin bonded glass fibers.
 51. A filter element as claimed in claim 34wherein each support and drainage layer comprises an extruded polymericmesh having a number of strands per inch of greater than about 30,wherein the first support and drainage layer is positioned upstream ofthe filter layer in a filtering environment for which the filter elementis adapted, wherein the cushioning layer comprises a nylon or polyesternonwoven material, and wherein the filter element further comprises awrap member spirally wrapped around the pleated composite with a gapbetween adjacent windings of the wrap.
 52. A filter element as claimedin claim 51 wherein the fibrous medium comprises resin bonded glassfibers.
 53. A filter element as claimed in claim 34 wherein each supportand drainage layer comprises polyester, polypropylene, or polyamide.